The conventional telecommunications network includes two distinct communication pathways or subnetworks—a voice network and a signaling network. These two networks function in a cooperative manner to facilitate a call between users. As implied by its name, the voice network handles the transmission of voice (or user data) information between users. The signaling network has a number of responsibilities, which include call setup, call teardown, and database access features. In simple terms, the signaling network facilitates the dynamic linking together of a number of discrete voice-type communication circuits, such that a voice-type connection is established between the calling and called party. These functions are generically referred to as call setup and call teardown. Additionally, the signaling network provides a framework through which non-voice related information may be transported, with this data and transport functionality being transparent to the users. This signaling technique is often referred to as out-of-band signaling, where the term “band” implies voice band. Common examples of services provided via the signaling network include 800 number database services, calling card verification services, and caller ID services. The original motivation for employing such an out-of-band signaling technique was to provide telecommunications service agents with an infrastructure that allowed for new and enhanced revenue producing services, such as 800 database access, call waiting, and caller ID services and to avoid tying up expensive voice trunks with signaling traffic.
From a hardware perspective, an SS7 network includes a plurality of SS7 nodes, generically referred to as signaling points (SPs), that are interconnected using signaling links, also referred to as SS7 links. At least three types of SPs are provided in an SS7 network: service switching points (SSPs), signal transfer points (STPs) and service control points (SCPs).
An SSP is normally installed in Class 4 tandem or Class 5 end offices. The SSP is capable of handling both in-band signaling and SS7 signaling. An SSP can be a customer switch, an end-office, an access tandem and/or a tandem. An STP transfers signaling messages from one signaling link to another. STPs are packet switches and are generally installed as mated pairs. Finally, SCPs control access to databases such as 800 number translation, 800 number carrier identification, credit card verification, etc. SCPs are also deployed in pairs.
Signaling links are transmission facilities used to connect SPs together. Conventional signaling links are dedicated bidirectional facilities operating at 56 kbps in the U.S. and Canada and at 64 kbps when clear channel capability is deployed. Normally, every link has a mate for redundancy and enhanced network integrity.
In order to ensure consistent and reliable communication across the signaling network infrastructure, a common or standard digital signaling protocol was established by the ITU-TS in the mid-'60s, and this protocol was known as Signaling System 6. By the mid-'80s the protocol had evolved into a slightly more sophisticated system known as Signaling System 7 (SS7). As a protocol, SS7 defines the hierarchy or structure of the information contained within a message or data packet. This internal data structure is often referred to as the protocol stack, which is comprised of a number of well defined strata or layers. In general terms, the SS7 protocol stack consists of 4 levels or layers:                (1) the physical layer        (2) the data link layer        (3) the network layer        (4) the user and application part layer        
The physical layer is the lowest or most fundamental layer and is the first layer that is used to interpret and process and incoming message. This layer is concerned with determining and/or providing the electrical characteristics needed to transmit the digital data over the interface being used. Following interpretation/processing, the incoming message is passed up the stack to the data link layer.
The data link layer (MTP layer 2) resides adjacent and above the physical layer and is responsible for providing the SS7 network with error detection/correction and properly sequenced delivery of all SS7 message packets. Following interpretation/processing, the incoming message is passed up the stack to the network layer.
The network layer (MTP layer 3) resides adjacent and above the data link layer and is responsible for message packet routing, message packet discrimination, and message packet distribution. Functionally, message discrimination determines to whom the message packet is addressed. If the message contains the local address (of the receiving node), then the message is passed on to message distribution. If the message is not addressed to the local node, then it is passed on to the message router. Following interpretation/processing, the incoming message is passed up the stack to the user part layer only if the message was destined to that node.
The user and application part layer resides adjacent and above the network layer and actually consists of several distinct parts. The parts may include mobile application part (MAP), radio access network application part (RANAP), transaction capabilities application part (TCAP), ISDN user part (ISUP), telephone user part (TUP), and broadband ISDN user part (B-ISUP).
While the SS7 network has functioned successfully for a number of years, such a network typically includes centralized nodes that make routing decisions which can have some disadvantages. Such disadvantages include expense due to processing requirements of centralized nodes, high-traffic volume at the centralized nodes, and possible network outage if one or more of the centralized nodes fails.
FIG. 1 is a block diagram of a conventional SS7 network in which a centralized node makes routing decisions. In FIG. 1, SSPs 100 and 102 communicate with SCPs 104 and 106 through a mated pair of STPs 108 and 110. STPs 108 and 110 are located at a central point in the network and receive traffic from many SSPs and SCPs. STPs 108 and 110 make routing decisions for SS7 messages and route the messages to their intended destinations. STPs 108 and 110 may also translate the protocol of incoming SS7 messages if the destination node is of a different protocol than the sending node.
Because of the central location of STPs 108 and 110 and because of all of the tasks required to be performed by STPs 108 and 110, STPs 108 and 110 include an extremely complex parallel architecture for handling all of these functions. An example of such an STP with a highly parallel architecture is the EAGLE® STP available from Tekelec of Calabasas, Calif.
FIG. 2 is a block diagram of a conventional data network. In the data network, routers 200, 202, 204, and 206 are co-located with end offices 208 and 210 and databases 212 and 214. Routers 200, 202, 204, and 206 are IP routers. Routers 200, 202, 204, and 206 are only capable of making IP routing decisions. Thus, packets incoming from elements 208, 210, 212, and 214 are in IP format and packets outcoming from routers 200, 202, 204, and 206 are also in IP format.
While IP networks provide a number of advantages, IP networks do not include the inherent reliability or stability of a conventional SS7 network. As discussed above, the conventional SS7 network architecture includes centralized routing elements which are expensive, complex, and subject to high-traffic volumes. Thus, there exists a need for a distributed SS7 gateway that avoids at least some of the difficulties associated with the prior art.